It turns out this was happening because the ISP had port security
enabled on our switch and they were shutting down the port when we
exceeded 5 MAC addresses. Been banging our heads for 2 days on this
one :)
Matei
> [ 825.940139] e1000e: eth0 NIC Link is Down
> [ 825.960899] vzbr0: port 1(eth0) entering disabled state
>> then, 300 seconds later (it is always 300s),
>> [ 1127.620861] e1000e: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow
> Control: None